We propose a three year program of investigation into the use of expert systems for the diagnosis of liver disease, using deep reasoning methods based on structure/function models. This research would lead to the refinement of our prototype system Pathex/Liver-1 for liver disease diagnosis. As part of this refinement process, techniques and methodologies of artificial intelligence will be used to investigate the problem-solving of experts in the diagnosis of liver disease. Specifically, research will be directed toward: 1. the expansion of the current Pathex/Liver-1 expert system in order to recommend diagnoses in a larger class of liver diseases and associated disorders. 2. the expansion of the current Pathex/Liver-1 expert system in order to increase the types of data it can gather. 3. The development of a deeper understanding of the representations and problem-solving methods needed to integrate structure/function models with traditional techniques for constructing medical knowledge-based systems, and 4. the continuing development of high level knowledge-engineering tools to support the implementation of medical diagnostic systems. The resulting prototype system Pathex/Liver-2 will represent a significant advance in the state of the art in medical knowledge- engineering demonstrating the way structure/function models may be integrated with compiled diagnostic knowledge to improve diagnostic reasoning performance. The high level knowledge-engineering tools developed will also represent an advance in the state of the art, representing a flexible, extensible, and modularized tools environment for representing and integrating diagnostic medical knowledge in other domains.